Electrostatic printing apparatus with inking means between electrodes



Jan. 24, 1967 HIROOMI SAWADA ET AL 3,299,806

ELECTROSTATIC PRINTING APPARATUS WITH INKING MEANS BETWEEN ELECTRODESFiled Feb. 16, 1965 trophotographic process.

United States Patent 3,299,896 ELECTRQSTATIC PEiNTlNG APPARATUS WITHINKIi G MEANS BETWEEN ELECTRODEQ Hiroomi Sawaila, Kenji Takahashi, KeizoKobayas h and Shigerii K3511, Tokyo, Japan, assignors to Dainippon inkand Chemicals, Incorporated, Itabashi-ku, Tokyo, Japan Filed Feb. 16,1965, Ser. No. 432,989 Claims priority, application Japan, Feb. 20,1964, 39/8,8ii5; Oct. 23, 1964, 39/59,914 3 Claims. (Cl. 101114) Thisinvention relates to a method of printing by means of electrostaticforce and an apparatus therefor. More particularly, the inventionrelates to a method of printing which comprises positioning below astencil the material to be imprinted, bringing electrically chargedpowdered ink close to the stencil, having a particle size such that itcan pass through the open areas of the stencil and by utilizing theelectrostatic force which acts between the electrically charged powderedink and the material to be imprinted, causing the adherence of theformer to the latter via the stencil in accordance with the pattern ofsaid stencil; and to a suitable apparatus to be used in such a method.

Numerous methods of imparting print to material to be imprinted areknown, screen printing being one of them. However, in accordance withthe conventional printing methods, inclusive of the usual screenprinting methods, there was always required a certain amount of printingpressure. Hence, when the surface unevenness of the material to beimpressed was pronounced, it was impossible to impart precise print tosuch a material.

An object of this invention is to provide a printing method andapparatus, which do not have the hereinbefore noted shortcoming.

Other objects of this invention will in part be obivous and will in partappear hereinafter.

These objects of the invention can be achieved by an operation andapparatus based on the following theory.

When powdered ink is temporarily adhered to the surface of a carryingmember, say, a roller, which has the function of carrying powdered inkand conveying it, an electric charge is imparted thereto by means ofcorona discharge, following which the roller is rotated to bring theelectrically charged powdered ink on the roller surface close to thematerial to be imprinted. The powdered ink separates from the roller bymeans of the electrosatic force which acts between the powdered ink andthe material to be imprinted, when the electrostatic force becomesgreater than the adhering force of the powdered ink to the roller andbecome transferred to the material to be imprinted. Now, by interposinga stencil between the roller and the material to be imprinted, part ofthe powdered ink which has left the roller pass through the open areasof the stencil while the passage of others are blocked, with theconsequence that a print is obtained on the material to be imprintedwhich is a configuration of the pattern of the open areas of stencil.Further, 'by affording mechanically a start to the transfer of thepowdered ink, its transferability is enhanced. The transferability isincreased also by the provision behind the rear side of the material tobe imprinted, of a grounded electrode plate or an electrode platecharged with a polarity opposite to that of the corona dischargeelectrode. However, when the material to be imprinted is one which,

per se, possesses a great electric capacity, the transferability isexcellent even though such an electrode is not provided.

As the powdered ink, preferred is the use of a pigmented resin powdersuch as the developer used in elec- After these have been adhered "iceto the material to be imprinted, they can be readily fixed thereto bymeans of heat or a solvent. Further, it is also possible to use apowdered carrier, such as a clay calcium carbonate, alumina, to whichdyes have been adhered temporarily, and after transferring this from thecarrying member to the material to be imprinted, to fix this alone tothe material, while eliminating the carrier.

As the carrying member, a means so set up by use of a material whosesurface is such that it can temporarily adhere and carry the powderedink, e.g., such as felt, flannel, velvet, astrakhan, mohair, shagg pile,brush, nonwoven fabric, woolen knit goods, buckskin, sponge andsynthetic rubber foam, will do. As an example, there can be used aroller whose surface is wrapped with these materials or an endless feltmade of these materials.

While preferably the screen stencil is made of material being relativelywell insulated, such as silk and the polyamide and polyester fibers,metal screens can also be used. The preparation of the printing stencilcan be done by the various methods that are usually practiced in screenprinting. When a high precision print is not required, i.e., when theinvention method is to be employed for, say, a simple stamping, thestencil may be simply a stencil of paper. The stencil and the materialto be imprinted can be disposed in spaced relationship to each other,for example, with a clearance of from 1 mm. to 1 cm. This is animportant feature of this invention, and it is for this reason that theprinting can be accomplished accurately, though no printing pressure atall is applied to the material to be imprinted. In this respect, thepresent invention can be regarded as having transcended the conventionalconcept of printing. It is, of course, permissible to dispose thestencil and the material to be ini printed in intimate contact with eachother. When it is intended to imprint an exact reproduction of thepattern of the stencil, the stencil and the material to be im printedmust be placed in parallel to each other, but when it is desired todistort the pattern, the material to be imprinted can be disposedobliquely with respect to the stencil orin a distorted position. In anyevent, however, it is preferred that the two are maintained in asubstantially parallel relationship to each other.

The accompanying drawings FIGS. 1, 2, 3 and 4 are schematic viewsillustarting embodiments of the apparatus and method of the presentinvention. The invention will be fully described below with reference tothese drawings.

In FIG. 1, a roller 2, which, while rotating in the direction of arrowX, is adapted to roll in the direction of arrow Y, is employed. Carryingroller 2 is equipped with a suitably designed feed means (not shown) bywhich the roller surface is fed constantly with a fresh supply ofpowdered ink 6 from a conventional powdered ink feeding means (notshown). Corona discharge electrode 1 also is so designed that it ismovable in the direction of arrow Z synchronously with the travel ofcarrying roller 2 in a horizontal direction (direction of arrow Y).These are, of course, adapted to roll, turn back and move in theopposite direction as well. Material to be imprinted 4 is placed belowstencil 3 in parallel thereto, and below the material to be imprinted 4is placed an electrode plate 5. Now when this apparatus is placed inoperation, powdered ink 6 carried by carrying roller 2 receives a chargeby means of a discharge from corona discharge electrode 1 in thevicinity of a point where it has approached nearest to the electrode andthen approaches the material to be imprinted 4 with the rotation ofcarrying roller 2. When the charged powdered ink 6 contacts stencil 3ordue to the electrostatic force which acts between the powdered ink andthe material to be imprinted 4, minute as it is it leaves carryingroller 2, passes through the open areas of the stencil 3, and adheres tothe material to be imprinted 4 to accomplish the printing. Hence, inaccordance with the embodiment shown in FIG. 1, printing is accomplishedon the material to be imprinted progressively as the carrying roller isrotated.

The apparatus can be designed so that the stencil is forcibly charged bymeans of such as, for example, a battery, electric capacitor, or othersuitable means so that a constant potential is maintained at all times.By designing the apparatus in this manner, a control can be had over theamount adhered of the powdered ink. The material for the stencil andscreen should be chosen from those having high conductivity such as themetals when an electric potential is to be applied, but otherwise thoseof relatively high resistivity such as silk, nylon and polyesters arepreferred.

The deposited powdered ink is then fixed to the imprinted material bymeans of heat or solvent vapor.

While the embodiment described with reference to FIG. 1 is the so-calledsheet-by-sheet printing method, the invention method can also be appliedto the continuous, high speed printing method. FIG. 2 shows one exampleof such an embodiment. Stencil 23 is made up in an endless belt fashion,and the carrying roller 22 and corona discharge electrode 21 aredisposed in such a fashion as to be encompassed by stencil 23. Materialto be imprinted 24 is moved continuously in the arrow directionslidingly over electrode plate 25. Stencil 23 is rotated in the arrowdirection, its speed being synchronized with that of the travel of thematerial to be imprinted 24. Carrying roller 22 also is rotated, thepowdered ink successively fed thereto as it rotates by a conventionalpowdered ink feeding means 22a and being charged by means of a dischargein the neighborhood of corona discharge electrode 21. The powdered inkthen is conveyed to the surface of stencil 23 from which it istransferred to the material to be imprinted 24, thus carying out theprinting operation continuously. The imprinted material then, afterproceeding through the fixing step, is either wound up or cut.

When the printing operation is carried out in accordance with themethods of FIGS. 1 and 2, the opportunity for the powdered ink to leavethe carrying roller is afforded by its contact with the stencil. Thus,even after the powdered ink has passed through the stencil, it issubjected to the influence of its scattering angle. Hence, when theclearance between the stencil and the material to be imprinted is great,there is a tendency for the print to become indistinct. This type oftrouble can be prevented by doing as follows. Namely, the stencil andthe material to be imprinted are interposed between two electrodes thatface each other. The powdered ink carrying member which is connected toa drive means by which it is driven is so disposed between the stenciland the electrode on the stencil side as to be capable of continuouslycirculating therebetween. Then, after setting up an electrostatic fieldbetween the two electrodes, the carrying member, which is caused tocirculate, is temporarily adhered with the powdered ink, followed bycharging the powdered ink with a corona discharge. The powdered inkwhich has a charge is then conducted along with the carrying member toabove the stencil where the powdered ink is moved towards the materialto be imprinted under the influence of the electrostatic field betweenthe two electrodes and is adhered to the material to be imprintedthrough the intermediary of the stencil. This embodiment of the presentinvention will be described with reference to FIG. 3.

In FIG. 3, 31 is the electrode on the stencil side while 32 is theelectrode on the material-to-be-imprinted side, the electrostatic fieldbeing set up at that part between A and B. Stencil 33 and the materialto be imprinted 34 is interposed in parallel fashion between the twoelectrodes 31 and 32. Since electrode 31 on the stencil side is formedby providing a conductive layer on the roller, by wrapping carryingmember 35 about the electrode 31,

as the roller is rotated the former circulates between the latter andstencil 33. Corona discharge electrode 36 is disposed close to thecarrying member. Corona discharge electrode 36 and electrodes 31 and 32are suitably connected to a direct current source, the grounding thereofbeing required. In FIG. 3, as the roller which carries carrying member35 and electrodes 31 on the stencil side is rolled in the direction ofarrow X or in the reverse direction, it is rolled over the stencil inthe direction of arrow Y or the reverse direction. Hence, coronadischarge electrode 36 is also designed to travel in the direction ofarrow Z or in reverse synchronously with the foregoing movement of theroller. It is of course also permissible to dispose a plurality of thecorona discharge electrodes in line.

When this apparatus is started up, first powdered ink 37 is fed from afeed means (not shown), then by being conveyed by means of the rotationof the roller receives a charge in the vicinity a point where the rollerhas come close to corona discharge electrode 36, and thereafter conveyedonto stencil 33. When the roller comes into contact with stencil 33 orimmediately therebefore, powdered ink 37 starts to leave carrying member35, pass through the open areas of the stencil 33 and become transferredto the material to be imprinted. Although the powdered ink is subjectedto such other external forces as its contact with the stencil and otherforces besides merely the electrostatic force, the external forces arepractically all eliminated by the influence of the electrostatic fieldbetween A and B, with the consequence that the powdered ink passesthrough stencil 33 perpendicularly and becomes adhered to the materialto be imprinted 34. Thus, the printing is accomplished accurately inconformance with the pattern of the stencil.

While the electrode on the stencil side in FIG. 3 is provided bywrapping a conductive layer about the roller, needless to say, when theroller itself is a conductor, it can be used as the electrode. However,when the roller itself is impressed with a voltage as in this case,there is the inconvenience that it must be completely insulated from theother means which are connected thereto. Hence, even in those caseswhere the roller itself is a con ductor, it is more convenient to wrapan insulator about it and then provide the conductive layer about thisinsulating material. This conductive layer (the electrode on the stencilside) usually consists of a metallic foil, though it also may be formed'by means of a paste of such as carbon, copper, silver, etc. In thosecases where the carrying member is made up in endless belt fashion, thestencil side electrode can be made up into a plate, roller or otheroptional forms. Alternatively, by providing the whole of the backside ofthe carrying belt with a conductive layer, this may be made to serve asthe stencil side electrode.

The electrode on the material-to-be-imprinted side is conveniently madeup in plate fashion, whereupon the material to be imprinted is placed.However, when the material to be imprinted has a sufiic-ient-ly greatelectric capacity or when it is a conductor and is grounded, since thematerial to be imprinted itself functions as the opposite electrode ofthat on the stencil side, it can be made to serve as the electrodewithout the need for especially providing a back plate. As the oppositeelectrode of that on the stencil side, the earth or that having anelectric capacity sutficient'ly equivalent thereto can be chosen. Thatis to say, the electrode on the material-to-be-imprinted side does notnecessarily have to be one which has been provided artificially. Ingeneral, however, it is preferred to provide an electrode plate wherebythe material to be imprinted is grounded as Well as to make it possibleto charge the material to be imprinted suitably by utilizing conductionor electrostatic induction.

The intensity and direction of the electrostatic field to be formedbetween the two electrodes must be determined to conform with themagnitude and polarity of the charge imparted to the powdered ink. Theelectrostatic field contributes to the property of the powdered ink toproceed in a straight line as well as in regulating its transferability.For example, if the stencil side electrode is charged with same polarityas that of the powdered ink and the direction of the electrostatic forceacting between the two electrodes faces towards the electrode on thematerial-to-be-imprinted side, the transferability of the powdered inkbecomes markedly good. On the other hand, if the polarity of the stencilside electrode is opposite to that of the powdered ink and the directionof the electrostatic force between the two electrodes faces towards thestencil side electrode, the transfer of the powdered ink is greatlyinhibited, if not completely prevented. Consequently, if the appliedvoltage is regulated between the electrodes, the desired transferabilitycan be obtained and the tone of the print becomes controllable.

As the printing according to this invention is accomplishedelectrostatically, the time required for the actual transfer of the inkis very short, if the mechanical functions are considered separately.Thus, according to the invention method, it becomes possible to carryout ultra high speed continuous printing operations. Continuous printingcan be practiced, for example, by means of an apparatus such as shown inFIG. 4.

In FIG. 4, a stencil 43 is made up in an endless belt fashion, andprovided such as to be encompassed thereby are endless belt-fashioncarrying member 45 and corona discharge electrode 46. Carrying member 45is supported by three rollers, one of the rollers 41 being impressedwith a DC. voltage, thus functioning as the electrode on the stencilside. Beneath stencil 43 and vis-a-vis the stencil side electrode isprovided the material-to-beimprinted side electrode 42. The material tobe imprinted 44, being delivered continuously from a hoop, is conveyedin the arrow direction slidingly over the material-to be-imprinted sideelectrode. The speed at which the material is conveyed is preferably aspeed in synchronism with the rotating speed of the stencil.

The powdered ink is fed to carrying member 45 by powdered ink feedingmeans 45a and is discharged by means of the discharge from coronadischarge electrode 46 and then conveyed to between stencil 43 and thestencil side electrode 41. The powdered ink is here, under the influenceof the electrostatic field produced by the two electrodes 41 and 42,transferred by means of the electrostatic ,force to the side of thematerial to be imprinted to accomplish the printing. After completion ofthe printing, the imprinted material 44, aft-er passing through a fixingmeans, is either wound up or out.

As fully described hereinabove, the present invention concerns a screenprinting method which utilizes electrostatic forces. The point in whichthe invention method differs from the conventional screen printingmethod is in that it can make an impression without contact orapplication of pressure. The fact that printing can be done withoutapplication of pressure, i.e., that an accurate impression can be madewith the powdered ink advancing in a straight line though there is somedistance separating the stencil from the material to be imprinted, meansthat precision printing can be done even though the material to beimprinted in one whose surface uneveness is unusually great. Further,the fact that printing can be done without application of pressure meansthat those material which are easily susceptible to deformation by meansof stress can also be imprinted. Thus, .in accordance with thisinvention, those materials which were hitherto regarded as impossible ofbeing imprinted, such as sponge, fabric, nonwoven fabric, paste,vegetable, =fruit, slate, foamed concrete, etc., can also be imprinted.For example, letters smaller than points can be printed with accuracyand beauty on such as 40-count broadcloth, corrugated nylon pile havingpiles 1 mm. long, embossed fabrics, etc., even though the material to beimprinted is separated by a distance greater than 5 mm. Further,although it is impossible by the usual methods to print letters of lessthan 2-3 cm. on the surface of, say, light weight foamed concrete knownby the trade name of Sipolex because of the unusual unevenness of itssurface, in accordance with the invention method, since the ink adheresaccurately along the uneven portions, the printing of letters of theorder of 1.2-1.5 mm. becomes possible. When the surface of the materialto be imprinted is smooth and flat, needless to say, still finerprinting can be accomplished. For example, in the case of such as glass,ceramics, metal, plastics and coated paper, the printing accurately ofletters less than 0.8 mm. is also possible. Particularly, in the casewhere the mode employed is that in which the powdered ink is transferredin a electrostatic field, this straight-line advancing property of theink is enhanced, with the consequence that the precision of printing isfurther enhanced. Hence, it be comes possible to accomplish themulticolored printing of photographs, which compares favorably withthose obtained conventionally.

What is claimed is:

1. An electrostatic printing method which comprises positioning amaterial to be imprinted on one side of an uncharged stencil, placing anelectrode plate adjacent the side of the said material to be imprintedremote from said stencil, bringing into contact with the stencil apowdered ink carrying member capable of moving past said stencil,providing another electrode on the opposite side of the ink carryingmember from the stencil and which is electrically insulated from thesaid carrying member in the neighborhood of the point where the saidcarrying member comes into contact with the stencil in a position suchthat the electrode is opposed to the electrode plate beneath thematerial to be imprinted with the stencil and the material to beimprinted between the electrode and electrode plate, establishing apotential difference between the electrode and the electrode plate,supplying a powdered ink to the said carrying member, electricallycharging the powdered ink on the said carrying member by applying acorona discharge thereto, bringing the said charged powdered ink ontothe stencil by moving the said carrying member, and passing the saidpowdered ink through openings of the stencil by means of an electrostatic force which acts between said powdered ink and said material tobe imprinted, whereby the said ink is adhered to the said material inaccordance with the pattern of the stencil.

2. An electrostatic printing apparatus comprising a rolling powdered inkcarrying member, powdered ink feeding means associated therewith forfeeding powdered ink to said carrying member, a corona dischargeelectrode adjacent said carrying member for charging said powdered inkcarried by said carrying member, an uncharged fixed stencil over whichsaid carrying member rolls, an electrode disposed on the opposite sideof said carrying member from the said stencil and being electricallyinsulated from said carrying member, an electrode plate disposed on theother side of said stencil from said carrying member, said electrodeplate being adapted to have the material to be imprinted placed thereon,and means coupled to said apparatus for establishing a potentialdifference between said electrode plate and the ink on said carryingmember.

3. An electrostatic printing apparatus comprising a rotating powderedink carrying member, powdered ink feeding means associated therewith forfeeding powdered ink to said carrying member, a corona dischargeelectrode adjacent said carrying member for charging the powdered inkcarried by said carrying member, an uncharged stencil traveling inendless fashion adjacent to said rotating carrying member, an electrodedisposed on the opposite side of said carrying member from said stenciland being electrically insulated from said carry- 7 ing member, anelectrode plate on the other side of said stencil from said carryingmember, means for carrying the material to be imprinted slidingly oversaid electrode plate, and means coupled to said apparatus forestablishing a potential difierence between said electrode plate and theink on said carrying member References Cited by the Examiner UNITEDSTATES PATENTS 2,725,304 11/1955 Landrigan et a1. 2,787,556 4/1957 Haas.

8 Jarcis. Darrel et a1. Bolton 118-637 Childress et a1 101-114 X Nail.Schwertz. Childress. Childress.

0 ROBERT E. PULFREY, Primary Examiner.

E. S. BURR, Assistant Examiner.

1. AN ELECTROSTATIC PRINTING METHOD WHICH COMPRISES POSITIONING AMATERIAL TO BE IMPRINTED ON ONE SIDE OF AN UNCHARGED STENCIL, PLACING ANELECTRODE PLATE ADJACENT THE SIDE OF THE SAID MATERIAL TO BE IMPRINTEDREMOTE FROM SAID STENCIL, BRINGING INTO CONTACT WITH THE STENCIL APOWDERED INK CARRYING MEMBER CAPABLE OF MOVING PAST SAID STENCIL,PROVIDING ANOTHER ELECTRODE ON THE OPPOSITE SIDE OF THE INK CARRYINGMEMBER FROM THE STENCIL AND WHICH IS ELECTRICALLY INSULATED FROM THESAID CARRYING MEMBER IN THE NEIGHBORHOOD OF THE POINT WHERE THE SAIDCARRYING MEMBER COMES INTO CONTACT WITH THE STENCIL IN A POSITION SUCHTHAT THE ELECTRODE IS OPPOSED TO THE ELECTRODE PLATE BENEATH THEMATERIAL TO BE IMPRINTED WITH THE STENCIL AND THE MATERIAL TO BEIMPRINTED BETWEEN THE ELECTRODE AND ELECTRODE PLATE, ESTABLISHING APOTENTIAL DIFFERENCE BETWEEN THE ELECTRODE AND THE ELECTRODE PLATE,SUPPLYING A POWDERED INK TO THE SAID CARRYING MEMBER, ELECTRICALLYCHARGING THE POWDERED INK ON THE SAID CARRYING MEMBER BY APPLYING ACORONA DISCHARGE THERETO, BRINGING THE SAID CHARGED POWDERED INK ONTOTHE STENCIL BY MOVING THE SAID CARRYING MEMBER, AND PASSING THE SAIDPOWDERED INK THROUGH OPENINGS OF THE STENCIL BY MEANS OF ANELECTROSTATIC FORCE WHICH ACTS BETWEEN SAID POWDERED INK AND SAIDMATERIAL TO BE IMPRINTED, WHEREBY THE SAID INK IS ADHERED TO THE SAIDMATERIAL IN ACCORDANCE WITH THE PATTERN OF THE STENCIL.